The present disclosure relates to a recording device that performs recording on an optical recording medium, and more particularly to a recording device configured to irradiate first light for performing mark recording and second light for performing position control on the basis of a position guide formed on the optical recording medium through a common object lens.
As an optical recording medium for recording and reproducing of signals by irradiation of light, a so-called optical disc such as CD (Compact Disc), DVD (Digital Versatile Disc), and BD (Blu-ray Disc: Registered Trademark) have come into use.
Concerning an optical recording medium taking a major role in of the next generation of the optical mediums relating to the currently widespread such as CD, DVD, and BD, the applicant proposes a so-called bulk recording type optical recording medium described in Japanese Unexamined Patent Application Publication Nos. 2008-135144 and 2008-176902.
For example, as shown in FIG. 19, bulk recording is to perform multilayer recording on a bulk layer 102 by performing laser beam irradiation while sequentially changing the focus position, an optical recording medium (a bulk type recording medium 100) having at least a cover layer 101 and a bulk layer (a recording layer) 102, which is a technique to achieve mass recording.
Concerning such bulk recording, in Japanese Unexamined Patent Application Publication No. 2008-135144, a recording technique which is a so called micro-hologram method is disclosed.
In the micro-hologram method, a so-called hologram recording material is used as a recording material of the bulk layer 102. As the hologram recording material, for example, a photopolymerization type photopolymer and the like have been widely used.
The micro-hologram method is broadly divided into two methods of a positive type micro-hologram method and a negative type micro-hologram method.
The positive type micro-hologram method is a method of condensing two opposed light fluxes (light flux A and light flux B) at the same position and forming a micro-interference pattern (hologram) to use the interference pattern as a recording mark.
As a reverse idea to the positive type micro-hologram method, the negative type micro-hologram method is a method of erasing a previously formed interference pattern by irradiation of laser to use the erased part as a recording mark. In the negative micro-hologram method, an initialization process for forming the interference pattern is performed in advance on the bulk layer 102 before a recording operation is performed. Specifically, as the initialization process, opposed light fluxes formed by parallel light are irradiated to form the interference pattern on the whole of the bulk layer 102.
After the interference pattern is formed by the initialization process as described above, information recording based on the forming of the erasure mark is performed. That is, the irradiation of laser is performed in a state of focusing on an arbitrary layer position, thereby performing the information recording based on the erasure mark.
As a method of bulk recording different from the micro-hologram method, the applicant also proposes, for example, a recording method of forming a void (vacancy or blank) disclosed in Japanese Unexamined Patent Application Publication No. 2008-176902, as a recording mark.
The void recording method is a method of performing irradiation of laser with relatively high power on the bulk layer 102 formed of a recording material such as photopolymerization type photopolymer, to record vacancy (void) in the bulk layer 102. As described in Japanese Unexamined Patent Application Publication No. 2008-176902, the vacancy part formed as described above has a refractive index different from that of the other part in the bulk layer 102, and it is possible to raise the reflexibility at such a boundary part. Accordingly, the vacancy part serves as a recording mark, and thus information recording based on the forming of the vacancy mark is realized.
Since such a void recording method is not to form the hologram, the irradiation of light from one side of recording may be performed. That is, it is not necessary to condense two light fluxes at the same position to form the recording mark in the same manner as the positive type micro-hologram method.
In comparison with the negative micro-hologram method, there is a merit in that the initialization process may not be necessary.
In Japanese Unexamined Patent Application Publication No. 2008-176902, an example of performing irradiation of pre-cure light before recording when performing the void recording is described. However, even when the irradiation of such pre-cure light may be omitted, the recording of void is possible.
The recording layer (bulk layer) of such a bulk type optical disc recording medium does not have an evident multilayer structure, for example, in meaning in which a plurality of reflection films are formed, although it is a bulk recording type (merely, referred to as bulk type) optical disc recording medium for which various recording methods are proposed as described above. That is, in the bulk layer 102, a reflection film and a guide trace for each recording layer, which a general multilayer disc has, are not provided.
Accordingly, in the state of the structure of the bulk type recording medium 100 shown in FIG. 19, focus servo or tracking servo may not be performed at the time of recording in which the mark is not formed.
For this reason, in practice, the bulk type recording medium 100 is provided with a referential reflection face (reference face) having guide traces as shown in FIG. 20.
Specifically, guide traces (position guide) are formed in a spiral shape or concentric shape, for example, by forming pits or grooves on the lower face side of the cover layer 101, and a selective reflection film 103 is formed thereon. On the lower layer side of the cover layer 102 on which the selective reflection film 103 is formed as described above, a bulk layer 102 is laminated as an intermediate layer 104 in the drawing through an adhesive material such as UV curable resin.
By forming the guide traces using the pits or grooves as described above, absolute position information (address information) such as radius position information and rotation angle information is recorded. In the following description, a face on which such guide traces are formed and the absolute position information is recorded (in this case, the forming face of the selective reflection film 103) is called “reference face Ref”.
After forming the medium structure as described above, in the bulk type recording medium 100, as shown in FIG. 21, servo laser light (merely referred to as servo light) as laser light for position control is irradiated, separately from laser light (hereinafter, referred to as recording and reproducing laser light, or merely recording and reproducing light) for recording (or reproducing) a mark.
As shown, the bulk type recording medium 100 is irradiated with the recording and reproducing laser light and the servo laser light through a common object lens.
In this case, if the servo laser light reaches the bulk layer 102, there may be an adverse effect on the mark recording in the bulk layer 102. For this reason, in the bulk recording method of the related art, laser light having a wavelength band different from that of the recording and reproducing laser light is used as the servo laser light, and the selective reflection film 103 having wavelength selectivity in which the servo laser light is reflected and the recording and reproducing laser light passes is provided as a reflection film formed on the reference face Ref.
Under the above-description presupposition, an operation at the mark recording time on the bulk type recording medium 100 will be described with reference to FIG. 21.
First, when multilayer recording is performed on the bulk layer 102 on which the guide trace or the reflection film is not formed, it is predetermined where is to be the layer position for recording the mark in the depth direction in the bulk layer 102 is to be. In the drawing, as the layer position (mark forming layer position: also referred to as information recording layer position) for forming the mark in the bulk layer 102, a case of setting a total of five information recording layer positions L of a first information recording layer position L1 to a fifth information recording layer position L5 is exemplified. As shown, the first information recording layer position L1 is set as a position separated from the selective reflection film 103 (reference face Ref) on which the guide traces are formed in a focus direction (depth direction) by a first offset of-L1. The second information recording layer position L2, the third information recording layer position L3, the fourth information recording layer position L4, and the fifth information recording layer position L5 are set as positions separated from the reference face Ref by a second offset of-L2, a third offset of-L3, a fourth offset of-L4, and a fifth offset of-L5, respectively.
During recording when the mark is not yet formed, the focus servo and the tracking servo on each layer position in the bulk layer 102 based on the reflection light of the recording and reproducing laser light may not be performed. Accordingly, focus servo control and tracking servo control of the object lens during recording are performed such that a spot position of the servo laser light follows the guide traces with respect to the reference face Ref on the basis of the reflection light of the servo laser light.
However, the recording and reproducing laser light is necessary to reach the bulk layer 102 formed on the lower side than the reference face Ref to record a mark. For this reason, in the optical system in this case, a recording and reproducing light focus mechanism for independently adjusting the focus position of the recording and reproducing laser light is provided separately from the focus mechanism of the object lens.
An outline of an optical system for performing the recording and reproducing of the bulk type recording medium 100 including the mechanism for independently adjusting the focus position of the recording and reproducing laser light is shown in FIG. 22.
In FIG. 22, the object lens also shown in FIG. 21 is changeable in position in the radial direction (tracking direction) of the bulk type recording medium 100 and in the direction (focus direction) of approaching to and receding from the bulk type recording medium 100 by a 2-axis actuator as shown.
In FIG. 22, the mechanism for independently adjusting the focus position of the recording and reproducing laser light corresponds to a focus mechanism (expander) in the drawing. Specifically, the focus mechanism as the expander includes a fixed lens and a movable lens maintained to be changeable in position in a direction parallel to the optical axis of the recording and reproducing laser light by a lens driving unit. The movable lens is driven by the lens driving unit, collimation of the recording and reproducing laser light incident to the object lens in the drawing is changed, and the focus position of the recording and reproducing laser light is thereby adjusted independently from the servo laser light.
As described above, the recording and reproducing laser light and the servo laser light have different wavelength bands. Accordingly, in the optical system in this case, the reflection light of the recording and reproducing laser light and the servo laser light from the bulk type recording medium 100 is divided into each system by a dichroic prism in the drawing (i.e., each reflection light detection can be independently performed).
Considering forward light, the dichroic prism has a function of synthesizing the recording and reproducing laser light and the servo light on the same axis and inputting them to the object lens. Specifically, in this case, the recording and reproducing laser light is reflected by a mirror through the expander as shown, then is reflected by the selective reflection face of the dichroic prism, and is input to the object lens.
Meanwhile, the servo laser light passes through the selective reflection face of the dichroic prism and is input to the object lens.
FIG. 23 is a diagram illustrating servo control at the reproducing time of the bulk type recording medium 100.
When the reproducing is performed on the recording medium 100 on which the mark recording has been already performed, it is not necessary to control the position of the object lens on the basis of the reflection light of the servo laser light in the same manner as the recording time. That is, at the reproducing time, the focus servo control and tracking servo control of the object lens may be performed on the basis of the reflection light of the recording and reproducing laser light, on the mark row formed at the information recording layer position L (referred to as information recording layer L at the reproducing time) that is the reproducing target.
In the bulk recording method described above, the bulk type recording medium 100 is irradiated with the recording and reproducing laser light for mark recording and reproducing and the servo light as the position control light through the common object lens (synthesizing on the same optical axis), then, at the recording time, the focus servo control and tracking servo control of the object lens are performed such that the servo laser light follows the position guide of the reference face Ref, and the focus position of the recording and reproducing laser light are separately adjusted by the recording and reproducing focus mechanism. Accordingly, even when the position guide is not formed in the bulk layer 102, the mark recording can be performed at the necessary position (depth direction and tracking direction) in the bulk layer 102.
At the reproducing time, the focus servo control and tracking servo control of the object lens based on the reflection light of the recording and reproducing laser light are performed such that the focus position of the recording and reproducing laser light follows the already recorded mark row, and thus it is possible to perform the reproducing of the mark recorded in the bulk layer 102.
When the bulk recording method described above is employed, a spot position deviation in the inner direction of the recording face occurs between the recording and reproducing laser light and the servo laser light due to the occurrence of a so-called skew (tilt) or the occurrence of lens shift of the object lens caused by disc eccentricity.
FIG. 24A and FIG. 24B schematically show the spot position deviation between the recording and reproducing laser light and the servo laser light caused by the occurrence of the skew.
In the non-skewed state shown in FIG. 24A, the spot positions of the servo laser light and the recording and reproducing laser light coincide in the inner direction of the recording face. On the contrary, a difference in the optical axis between the servo laser light and the recording and reproducing laser light occurs according to the occurrence of the skew as shown in FIG. 24B, and a spot position deviation Δx shown in the drawing occurs.
FIG. 25A and FIG. 25B schematically show the spot position deviation between the recording and reproducing laser light and the servo laser light caused by the lens shift.
In the non-lens shift state shown in FIG. 25A, the object lens is at the reference position, and the center of the object lens and the optical axis c of each laser light incident to the object lens coincide with each other. The optical system is designed such that the spot positions in the inner direction of the recording face of each laser light coincide in the state where the object lens is at the reference position as described above.
On the contrary, when the object lens is shifted from the reference position to follow the disc eccentricity as shown in FIG. 25B by the tracking servo control (in this case, shifted to the left on paper), the spot position deviation Δx shown in the drawing occurs.
The spot position deviation caused by the lens shift occurs due to the difference in the incidence shapes of the servo laser light and the recording and reproducing laser light with respect to the object lens. Specifically, it is because the servo laser light is incident to the object lens by substantially parallel light, and the recording and reproducing laser light is incident by unparallel light.
According to the occurrence of the spot position deviation in the servo laser light and the recording and reproducing laser light caused by the skew or lens shift, difference in the information recording position in the bulk layer 102 occurs. That is, as can be understood from the above description, the spot position of the recording and reproducing laser light during recording is controlled by performing the tracking servo control of the object lens based on the reflection light of the servo laser light, and thus the recording may not be performed at the intended position in the bulk layer 102 according to the spot position deviation described above.
The information recording positions may be overlapped between the adjacent tracks according to the setting of the amount of skew eccentricity or track pitches (intervals of formation position guides). Specifically, the disc eccentricity or skew is due to the manner in which the disc is clamped to the spindle motor and may occur in different manners whenever the disc is loaded. Accordingly, for example, if rewriting based on disc shifting is performed on the disc, the shape of the skew eccentricity occurring at the previous recording time and the shape of the skew eccentricity occurring at the rewriting time are different. As a result, there is a problem that an overlap between the mark row of the recorded part and the mark row of the rewriting part occurs or they intersect with each other according to the case.
As described above, it is difficult to rightly reproduce the reproducing signal.
As one method for preventing the overlap of the mark rows or the intersection from occurring, the track pitches may be set wide on the reference face Ref.
However, when the track pitches of the reference face Ref are widened, obviously, the recording capacity in the bulk layer 102 is reduced.
Examples of the related art are disclosed in Japanese Unexamined Patent Application Publication Nos. 2009-9635, 2009-140568, and 2009-163811.
As one method for preventing the reduction of the recording capacity of the bulk layer 102 while preventing the overlap of the recording mark rows or the intersection caused by the skew or lens shift described above from occurring, there is a so-called self-tracking method.
The self-tracking is a technique for preventing the overlap or intersection of the recording mark rows on the recording layer on which the position guide is not formed, in which a side beam is generated and irradiated at a position that is an inner circumferential side with a light beam taking in charge of recording, and tracking servo is started with the side beam on the recorded mark row to continue recording after the first cycle recording such that the mark forming intervals of the marks with respect to the mark rows on which the recording is completed for the later cycle are kept at the interval between the recording beam spot and the side spot, thereby preventing the overlap or intersection of the mark rows from occurring.
FIG. 26A and FIG. 26B are diagrams illustrating a specific recording operation when such a self-tracking method is applied to bulk recording.
In the drawing, a spot S-sv&S-rpM based on a patterned circle indicates a spot S-sv of servo laser light and a main beam spot (recording beam spot) S-rpM of the recording and reproducing laser light. As described above, since the servo laser light and the recording and reproducing laser light are irradiated such that the optical axes thereof coincide, it may be indicated that the spot S-sv and the spot S-rpM overlap with each other in a direction parallel to the inner direction of the recording face (when the skew or lens shift does not occur).
The spot S-rpS shown by the white circle becomes the side beam spot generated using, for example, grating or the like, with respect to the recording and reproducing laser light.
The broken line in the drawing indicates a track (guide trace) formed on the reference face Ref.
FIG. 26A schematically shows a shape when the first cycle recording is performed.
In the first cycle recording, recording of the mark row based on the main beam spot S-rpM is performed while performing the tracking servo of the servo laser light on the track formed on the reference face Ref.
In the drawing, the track (broken line) on the reference face Ref and the actually recorded mark row (solid line) do not coincide. This is because it indicates that a spot position deviation occurs by the skew or lens shift occurs.
When the recording of one cycle track is performed as described above, the side beam spot S-rpS is positioned in the vicinity of the recorded mark row (mark row of the first cycle start position), in the vicinity of the first cycle completion position as shown in FIG. 26B.
The amount of occurrence of a bending state or disc eccentricity is equivalent when the radius position on the disc or the rotation angle position is equivalent. Accordingly, from this point, the side beam spot S-rpS is positioned in the vicinity of the recorded mark row of the first cycle as described above at the completion time of the recording of the first cycle.
In the vicinity of the recording completion of the first cycle, drawing-in of the tracking servo with respect to the mark row on which the first cycle recording is completed by the side beam spot S-rpS is performed, and the tracking servo of the object lens is thereby switched from the tracking servo based on the beam spot S-sv of the general servo laser light to the tracking servo using the side beam spot S-rpS.
Accordingly, the mark rows of the second cycle or later are formed at positions getting far away by a distance between the main beam spot S-rpM and the side beam spot S-rpS with respect to the recorded mark row formed on the inner circumferential side thereof, to prevent the overlap or intersection of the mark rows from occurring.
When the self-tracking method as described above is used, it is important that the amount of deviation in the position of the information recording layer when the first cycle recording is completed is substantially the same in the first cycle and the second cycle.
As described above, the amount of occurrence of the bending state or the disc eccentricity is substantially equivalent when the radius position on the disc or the rotation angle is substantially the same. Accordingly, generally, it is difficult to think that the difference in the information recording positions of the first cycle and the second cycle gets larger at the completion time of the first cycle recording.
However, in practice, the difference in the positions between the servo laser light and the recording and reproducing laser light does not occur according to only the eccentricity or the bending state of the disc, but occurs also due to the occurrence of deterioration of a slide mechanism sliding the whole of an optical pickup or occurrence of disturbance.
When a relatively large difference in the spot position caused by the deterioration of the slide mechanism or the disturbance occurs in the vicinity of the recording completion time point of the first cycle, the recording mark row of the second cycle may greatly deviate from the recorded mark row to the outer circumferential side at the recording completion time of the first cycle as shown in FIG. 27A, or, on the contrary, the overlap with the recorded mark row may occur as shown in FIG. 27B.
Even in any case of FIG. 27A and FIG. 27B, it is difficult to perform the drawing-in of the tracking servo on the recorded mark row of the first cycle by the side beam spot S-rpS in the vicinity of the recording completion of the first cycle. As a result, it is difficult to perform the switching to the recording based on the self-tracking.